Heat exchanger

ABSTRACT

A brazing material in a paste form is applied to dented portions formed on the outer surface of a core pipe, and then a pipe is disposed on the pipe, and brazing in a furnace. In this way, the brazing material that was melted by the heat will be reliably poured into the dented portions and bonded thereto after being cooled down. Thus, the dented portions formed on the outer surface of the core pipe can be reliably filled with the brazing material, which consequently eliminates a poor contact between the core pipe and the winding pipe. In addition, even if the wall thickness of portions in which projections are formed are made thinner in the process of forming the projections, the dented portions formed on the outer surface are filled with the brazing material, so that the core pipe thickness can be reinforced, and the reduction in strength of the portions with the projections can be prevented.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger. More specifically,the present invention relates to a heat exchanger including a core pipehaving projections that are formed on the inner surface thereof bypressing the outer surface of the core pipe, and a winding pipe that iswound around the outer surface of the core pipe.

BACKGROUND OF THE INVENTION

Some heat exchangers used for air conditioners, water heaters, and thelike are provided with a core pipe that forms a passage for a firstfluid, a winding pipe that is wound around the outer surface of the corepipe and forms a passage for a second fluid, and a heat exchanger thatexchanges heat between the first fluid and the second fluid. Forexample, as disclosed in JP-A Publication No. S51-105158, a double pipeheat exchanger is used as a heat exchanger for a water heater such as aheat pump water heater. Such a heat exchanger is formed by two pipes: acore pipe through which water flows and a winding pipe through which therefrigerant flows. These two pipes are spirally wound into an oval shapeand used as one heat exchanger unit, and a main body of the heatexchanger is formed by mutually superposing and connecting a number ofsuch heat exchanger units to each other. In addition, another technologyhas been proposed to improve the heat transfer performance of a heattransfer tube used in a heat exchanger. With this technology,projections are provided on the inner surface of the heat transfer tubeby pressing the outer surface of the heat transfer tube so as to improvethe heat transfer performance (JP-A Publication No. H06-70556).

SUMMARY OF THE INVENTION Problem the Invention is to Solve

However, when a core pipe having projections that are formed on theinner surface thereof by pressing the outer surface of the core pipe isused for a heat exchanger, such a core pipe has dents that are formed onthe outer surface thereof at portions corresponding to the projectionson the inner surface. When a winding pipe is wound around the core pipeand then the core pipe is spirally wound into an oval shape, since across-section of the core pipe has an irregular shape because of theprojections, there is a risk that a poor contact will be formed betweenthe core pipe and the winding pipe, which may consequently reduce theheat transfer performance. In addition, the wall thickness of projectingportions of the core pipe may be made thinner in a process of formingthe projections than the wall thickness of non-projecting portions ofthe core pipe, which may consequently reduce the strength of theprojecting portions.

Therefore, an object of the present invention is to overcome the aboveproblem and to improve the heat transfer performance of a heat exchangerincluding a core pipe having projections that are formed on the innersurface thereof by pressing the outer surface of the core pipe, and awinding pipe that is wound around the outer surface of the core pipe.

Means to Solve the Problem

A heat exchanger according to a first aspect of the present invention isa heat exchanger that exchanges heat between a first fluid and a secondfluid, the heat exchanger including a core pipe, a winding pipe, and abrazing material. Here, the core pipe forms a passage of a first fluid,and the core pipe has projections that are formed on the inner surfacethereof by pressing the outer surface of the core pipe and also hasdented portions on the outer surface thereof. The winding pipe forms apassage of a second fluid, and the winding pipe is wound around theouter surface of the core pipe. The brazing material is poured into thedented portions located in the vicinity of the winding pipe.

Here, the core pipe having the projections on the inner surface thereofis used. Because of the projections, the heat transfer performance ofthe core pipe is improved. At the same time, dents are formed on theouter surface of the core pipe at portions corresponding to theprojections that are formed on the inner surface of the core pipe. Inorder to eliminate a poor contact between the core pipe and the windingpipe when the winding pipe is wound around these dented portions, thebrazing material is poured into the dented portions located in thevicinity of the winding pipe. In this way, when the brazing material ispoured into the dented portions, the dented portions formed on the outersurface of the core pipe are filled with the brazing material, whichconsequently eliminates a poor contact between the core pipe and thewinding pipe.

Note that when the brazing material is poured into the dented portionslocated in the vicinity of the winding pipe, these dented portions arefilled with the brazing material. Therefore, even if the wall thicknessof projecting portions of the core pipe is made thinner in the processof forming the projections than the wall thickness of non-projectingportions of the core pipe, the core pipe thickness can be reinforced,and thus the reduction in strength of the projecting portions can beprevented.

A heat exchanger according to a second aspect of the present inventionis the heat exchanger described above, in which the brazing material isa brazing material in a paste form, which is applied to the dentedportions of the core pipe in advance and then melted and bonded thereto.

Here, the brazing material in a paste form is applied to the dentedportions of the core pipe in advance, and then brazing is carried out,for example, in a furnace. In this way, the brazing material melted bythe heat is reliably poured into the dented portions and bonded theretoafter being cooled down. Thus, the dented portions formed on the outersurface of the core pipe can be reliably filled with the brazingmaterial, which consequently eliminates a poor contact between the corepipe and the winding pipe. In addition, even if the wall thickness ofprojecting portions of the core pipe is made thinner in the process offorming the projections than the wall thickness of non-projectingportions of the core pipe, the dented portions formed on the outersurface of the core pipe are filled with the brazing material, and thecore pipe thickness can be reinforced, thus the reduction in strength ofthe projecting portions can be prevented.

A heat exchanger according to a third aspect of the present invention isthe heat exchanger described above, in which the brazing material is abrazing material in a linear form, which is disposed between the corepipe and the winding pipe in advance and then is melted and bondedthereto.

Here, the brazing material is disposed between the core pipe and thewinding pipe in advance, and then brazing is carried out, for example,in a furnace. The dented portions work in a similar way as a capillarytube. The brazing material melted by the heat is poured into the dentedportions due to the capillary force. Thus, a complicated process ofapplying the brazing material for each dented portion can be avoided,which results in improving the brazing efficiency. In addition, thebrazing material that was melted by the heat is reliably poured into thedented portions and bonded thereto after being cooled down. Thus, thedented portions formed on the outer surface of the core pipe can bereliably filled with the brazing material, which consequently eliminatesa poor contact between the core pipe and the winding pipe. In addition,even if the wall thickness of projecting portions of the core pipe ismade thinner in the process of forming the projections than the wallthickness of non-projecting portions of the core pipe, the dentedportions formed on the outer surface of the core pipe are filled withthe brazing material, so that the core pipe thickness can be reinforced.

A heat exchanger according to a fourth aspect of the present inventionis the heat exchanger described above, wherein the brazing material is abrazing material in a linear form, which is disposed on the winding pipewound around the core pipe and then melted and bonded thereto.

Here, the brazing material is disposed on the winding pipe wound aroundthe core pipe, and then brazing is carried out, for example, in afurnace. For example, when the core pipe is provided with helicallyarranged projections and the winding pipe is also helically wound aroundthe outer surface of the core pipe, it will be difficult to dispose abrazing material between the core pipe and the winding pipe in advance.Therefore, the brazing material in a linear shape is first disposed onthe winding pipe wound around the core pipe, and then brazing is carriedout. Also in this case, the brazing material that is melted by the heatwill be poured into the dented portions due to the capillary force.Thus, a complicated process of applying the brazing material for eachdented portion can be avoided, which results in improving the brazingefficiency. In addition, the brazing material that was melted by theheat is reliably poured into the dented portions and bonded theretoafter being cooled down. Thus, the dented portions formed on the outersurface of the core pipe can be reliably filled with the brazingmaterial, which consequently eliminates a poor contact between the corepipe and the winding pipe. In addition, even if the wall thickness ofprojecting portions of the core pipe is made thinner in the process offorming the projections than the wall thickness of non-projectingportions of the core pipe, the dented portions formed on the outersurface of the core pipe are filled with the brazing material, so thatthe core pipe thickness can be reinforced.

A heat exchanger according to a fifth aspect of the present invention isthe heat exchanger described above, in which the brazing material is abrazing material in a paste form, which is applied to the winding pipewound around the core pipe in advance and then melted and bondedthereto.

Here, the brazing material in a paste form is applied to the windingpipe wound around the core pipe, and then brazing is carried out, forexample, in a furnace. As a result, the same effect as in the fourthaspect can be obtained.

Effect of the Invention

As described above, the following effects can be obtained according tothe present invention.

With the heat exchanger according to the first aspect of the presentinvention, the core pipe having the projections on the inner surfacethereof is used. Because of the projections, the heat transferperformance of the core pipe is improved. At the same time, dents areformed on the outer surface of the core pipe at portions correspondingto the projections that are formed on the inner surface of the corepipe. In order to eliminate a poor contact between the core pipe and thewinding pipe when the winding pipe is wound around these dentedportions, a brazing material is poured into the dented portions locatedin the vicinity of the winding pipe. In this way, when the brazingmaterial is poured into the dented portions, the dented portions formedon the outer surface of the core pipe can be reliably filled with thebrazing material, which consequently eliminates a poor contact betweenthe core pipe and the winding pipe. In addition, even if the wallthickness of projecting portions of the core pipe is made thinner in theprocess of forming the projections than the wall thickness ofnon-projecting portions of the core pipe, the dented portions formed onthe outer surface of the core pipe are filled with the brazing material,and the core pipe thickness can be reinforced, thus the reduction instrength of the projecting portions can be prevented.

With the heat exchanger according to the second aspect of the presentinvention, the brazing material in a paste form is applied to the dentedportions of the core pipe in advance, and then brazing is carried out,for example, in a furnace. In this way, the brazing material melted bythe heat is reliably poured into the dented portions and bonded theretoafter being cooled down. Thus, the dented portions formed on the outersurface of the core pipe can be reliably filled with the brazingmaterial, which consequently eliminates a poor contact between the corepipe an d the winding pipe. In addition, even if the wall thickness ofprojecting portions of the core pipe is made thinner in the process offorming the projections than the wall thickness of non-projectingportions of the core pipe, the dented portions formed on the outersurface of the core pipe are filled with the brazing material, and thecore pipe thickness can be reinforced.

With the heat exchanger according to the third aspect of the presentinvention, the brazing material is disposed between the core pipe andthe winding pipe in advance, and then brazing is carried out, forexample, in a furnace. The dented portions work in a similar way as acapillary tube. The brazing material melted by the heat is poured intothe dented portions due to the capillary force. Thus, a complicatedprocess of applying the brazing material for each dented portion can beavoided, which results in improving the brazing efficiency. In addition,the brazing material that was melted by the heat is reliably poured intothe dented portions and bonded thereto after being cooled down. Thus,the dented portions formed on the outer surface of the core pipe can bereliably filled with the brazing material, which consequently eliminatesa poor contact between the core pipe and the winding pipe. In addition,even if the wall thickness of projecting portions of the core pipe ismade thinner in the process of forming the projections than the wallthickness of non-projecting portions of the core pipe, the dentedportions formed on the outer surface of the core pipe are filled withthe brazing material, so that the core pipe thickness can be reinforced.

With the heat exchanger according to the fourth aspect of the presentinvention, the brazing material is disposed on the winding pipe woundaround the core pipe, and then brazing is carried out, for example, in afurnace. For example, when the core pipe is provided with helicallyarranged projections and the winding pipe is also helically wound aroundthe outer surface of the core pipe, it will be difficult to dispose abrazing material between the core pipe and the winding pipe in advance.Therefore, the brazing material in a linear shape is first disposed onthe winding pipe wound around the core pipe, and then brazing is carriedout. Also in this case, the brazing material that is melted by the heatwill be poured into the dented portions due to the capillary force.Thus, a complicated process of applying the brazing material for eachdented portion can be avoided, which results in improving the brazingefficiency. In addition, the brazing material that was melted by theheat is reliably poured into the dented portions and bonded theretoafter being cooled down. Thus, the dented portions formed on the outersurface of the core pipe can be reliably filled with the brazingmaterial, which consequently eliminates a poor contact between the corepipe and the winding pipe. In addition, even if the wall thickness ofprojecting portions of the core pipe is made thinner in the process offorming the projections than the wall thickness of non-projectingportions of the core pipe, the dented portions formed on the outersurface of the core pipe are filled with the brazing material, so thatthe core pipe thickness can be reinforced.

With the heat exchanger according to the fifth aspect of the presentinvention, the brazing material in a paste form is applied to thewinding pipe wound around the core pipe, and then brazing is carriedout, for example, in a furnace. As a result, the dented portions formedon the outer surface of the core pipe can be reliably filled with thebrazing material, which consequently eliminates a poor contact betweenthe core pipe and the winding pipe. In addition, even if the wallthickness of projecting portions of the core pipe is made thinner in theprocess of forming the projections than the wall thickness ofnon-projecting portions of the core pipe, the dented portions formed onthe outer surface of the core pipe are filled with the brazing material,so that the core pipe thickness can be reinforced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a heat pump water heater in accordancewith the present invention.

FIG. 2 is a schematic diagram of a water heat exchanger in accordancewith the present invention.

FIG. 3 is a plan view of a core pipe in accordance with the presentinvention.

FIG. 4 is an enlarged view of section A-A in FIG. 3 in accordance withthe present invention.

FIG. 5 illustrates a brazing material that is melted and bondedaccording to a first embodiment in accordance with the presentinvention.

FIG. 6 illustrates a brazing material that is melted and bonded toaccording a second embodiment in accordance with the present invention.

FIG. 7 illustrates a brazing material that is melted and bonded toaccording a third embodiment in accordance with the present invention.

FIG. 8 illustrates a brazing material that is melted and bonded toaccording a fourth embodiment in accordance with the present invention.

DESCRIPTION OF THE REFERENCE SYMBOLS  1 hot water supply unit 100 heatpump water heater  2 heat pump unit  30 water heat exchanger  31, 41,51, 61, 71 core pipe 311 water inlet 312 water outlet 313, 413, 513,613, 713 projections 314, 414, 514, 614, 714 dented portion  32, 42, 72winding pipe  33, 43, 53, 63 brazing material  52, 62 straight pipe

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

The heat exchanger according to the present invention will now bedescribed based on the attached drawings and the embodiments. FIG. 1 isa schematic diagram of a heat pump water heater in which a heatexchanger of the present invention is employed. In the heat pump waterheater shown in FIG. 1, water is heated in a single pass from about 10°C. to about 90° C. over a long period of time in order to efficientlyuse low-cost nighttime electric power. Here, the heat pump water heaterincludes a hot water supply unit 1, and a heat pump unit 2. Thefollowing are successively coupled in the hot water supply unit 1: aservice water pipe 11, a hot water storage tank 12, a water circulationpump 13, a water supply pipe 3, a core pipe 31 that constitutes a waterheat exchanger 30, a hot water pipe 16, a mixing valve 17, and a hotwater supply pipe 18. Here, service water is supplied from the watersupply pipe 11 to the hot water storage tank 12. Low temperature wateris supplied by the water circulation pump 13 from the bottom part of thehot water storage tank 12 to the core pipe 31 of the water heatexchanger 30, and heated. The heated hot water flows into the upper partof the hot water storage tank 12. The high temperature hot water thatexits from the upper part of the hot water storage tank 12 via the hotwater pipe 16 is mixed with the cold water of a mixed water pipe 19 bythe mixing valve 17. This mixing valve 17 regulates the temperature ofthe supplied hot water, which is supplied to the user by the hot watersupply pipe 18.

Next, the heat pump unit 2 is provided with a refrigerant circulatingcircuit that includes a compressor 21, the water heat exchanger 30, anexpansion valve 23, and an air heat exchanger 24, which are connectedsequentially by a winding pipe 32. The refrigerant is compressed to ahigh pressure by the compressor 21, and is then sent to the water heatexchanger 30. The refrigerant whose heat was exchanged in the water heatexchanger 30 passes through the expansion valve 23, and is supplied tothe air heat exchanger 24. The refrigerant absorbs heat from thesurroundings, and then circulates back to the compressor 21.

FIG. 2 is a schematic diagram of the water heat exchanger 30 in the heatpump water heater. As shown in FIG. 2, the water heat exchanger 30includes the core pipe 31 and the winding pipe 32. The core pipe 31 isspirally formed into an oval shape in the same plane, and forms a waterpassage W. The winding pipe 32 is helically wound around the outercircumference of the core 31, and forms a refrigerant passage R.Further, the outer circumferential side of the spiral of the core pipe31 is a water inlet 311, and the center side of the spiral of the heattransfer pipe 31 is a water outlet 312. In the water heat exchanger 30,the refrigerant inside the winding pipe 32 flows into the refrigerantinlet 322 from the A22 direction, and radiates heat. Subsequently, therefrigerant flows out of the refrigerant outlet 321 in the A21direction. The service water supplied into the water inlet 311 from theA11 direction is heated by this heat, turns into hot water, and flowsout of the water outlet 312 in the A12 direction.

Next the core pipe 31 is described. As shown in FIG. 3, this embodimentuses the core pipe 31 having an inside diameter D of 8 mm in whichprojections each having a height H1 of 1 mm are provided verticallysymmetric at a 20 mm pitch in the pipe axial direction on the pipe innersurface. FIG. 3 illustrates only projections 313 provided upward whenviewed from the paper surface direction. In addition, flat surface parts31 a that are not provided with the projections exist on the innersurface of the core pipe 31. Accordingly, the heat transfer coefficientis improved because of the projections 313 provided inside the pipe,which consequently improves the overall performance of the heatexchanger.

FIG. 4 is an enlarged view of cross section A-A of one of theprojections 313 provided inside the core pipe 31 in FIG. 3. Here, as forthe core pipe 31, when the wall thickness is compared between the flatsurface parts 31 a in which the projections are not formed and portionsin which the projections 313 are formed, the wall thickness of theportions in which the projections 313 are formed is thinner. At suchportions of the core pipe, where the wall thickness is thinner, thestrength of the pipe wall may be reduced.

Therefore, as shown in FIG. 5, with the heat exchanger 30 in which aplurality of winding pipes 32, 32 are helically wound around the corepipe 31, a brazing material 33 in a linear form is first disposed on thewinding pipes 32, 32, and then brazing is carried out in a furnace (notshown). Here, the plurality of winding pipes 32, 32 are helically woundaround the core pipe 31, and the core pipe 31 is provided with theprojections 313 that are helically arranged. Consequently, it will bedifficult to dispose a brazing material between the core pipe and thewinding pipe in advance. Therefore, the brazing material 33 in a linearform is first disposed on the plurality of winding pipes 32, 32 woundaround the core pipe 31, and then brazing is carried out. In this case,the brazing material 33 melted by the heat is poured into dentedportions 314 due to the capillary force. Consequently, with the heatexchanger in which the plurality of winding pipes 32, 32 are helicallywound around the core pipe 31, it is possible to improve the brazingefficiency. In addition, the brazing material melted by the heat isreliably poured into the dented portions and bonded thereto after beingcooled down. Thus, the dented portions formed on the outer surface ofthe core pipe can be reliably filled with the brazing material, whichconsequently eliminates a poor contact between the core pipe and thewinding pipe. In addition, even if the wall thickness of projectingportions of the core pipe is made thinner in the process of forming theprojections than the wall thickness of non-projecting portions of thecore pipe, the dented portions formed on the outer surface of the corepipe are filled with the brazing material, and the core pipe thicknesscan be reinforced, thus the reduction in strength of the projectingportions can be prevented.

Second Embodiment

In a second embodiment, as shown in FIG. 6, with the heat exchanger inwhich a plurality of winding pipes 42, 42 are helically wound around acore pipe 41, a brazing material 43 in a paste form, which is containedin a container 45, is applied to the winding pipes 42, 42, and thenbrazing is carried out in a furnace (not shown). In this case, thebrazing material 43 melted by the heat will be poured into dentedportions 414 due to the capillary force. Consequently, with the heatexchanger in which the plurality of winding pipes 42, 42 are helicallywound around the core pipe 41, it is possible to improve the brazingefficiency. In addition, the brazing material melted by the heat isreliably poured into the dented portions and bonded thereto after beingcooled down. Thus, the dented portions formed on the outer surface ofthe core pipe can be reliably filled with the brazing material, whichconsequently eliminates a poor contact between the core pipe and thewinding pipe. In addition, even if the wall thickness of projectingportions of the core pipe is made thinner in the process of forming theprojections than the wall thickness of non-projecting portions of thecore pipe, the dented portions formed on the outer surface of the corepipe are filled with the brazing material, and the core pipe thicknesscan be reinforced, thus the reduction in strength of the projectingportions can be prevented.

Third Embodiment

In third embodiment, as shown in FIG. 7, a heat transfer tube 52 thatforms a refrigerant passage R is not a winding pipe but a straight pipe.In other words, with a heat exchanger 50, a straight pipe 52 that formsthe refrigerant passage R is disposed on the outer surface of a corepipe 51 that forms a water passage W. Here, a brazing material 53 in apaste form is applied in advance to dented portions 514 formed on theouter surface of the core pipe 51, and a straight pipe 52 is disposed onthe core pipe 51, then brazing is carried out in a furnace (not shown).In this way, the brazing material 53 melted by the heat is reliablypoured into the dented portions 514 and bonded thereto after beingcooled down. Thus, the dented portions 514 formed on the outer surfaceof the core pipe 51 can be reliably filled with the brazing material 53,which consequently eliminates a poor contact between the core pipe 51and the pipe 52. In addition, even if the wall thickness of portionswith projections 513 are made thinner in the process of forming theprojections, the dented portions 514 formed on the outer surface of thecore pipe 51 are filled with the brazing material 53, so that the corepipe thickness can be reinforced. Thus the reduction in strength of theportions with the projections 513 can be prevented.

Fourth Embodiment

Further, in a fourth embodiment, as shown in FIG. 8, a heat transfertube 61 that forms a refrigerant passage R is not a winding pipe but astraight pipe. In other words, with a heat exchanger 60, a straight pipe61 that forms the refrigerant passage R is disposed on the outer surfaceof the core pipe 61 that forms a water passage W. Here, a brazingmaterial 63 is disposed between a core pipe 61 and the straight pipe 61in advance, and then brazing is carried out in a furnace (not shown).Dented portions 614 work in a similar way as a capillary tube. Thebrazing material 63 melted by the heat is poured into the dentedportions 614 due to the capillary force. Thus, a complicated process ofapplying the brazing material for each dented portion can be avoided,which results in improving the brazing efficiency. In addition, thebrazing material 63 melted by the heat is reliably poured into thedented portions 614 and bonded thereto after being cooled down. Thus,the dented portions 614 formed on the outer surface of the core pipe 61can be reliably filled with the brazing material 63, which consequentlyeliminates a poor contact between the core pipe 61 and the straight pipe62.

1. A heat exchanger configured to exchange heat between a first fluidand a second fluid, comprising: a core pipe having a passage forcommunicating a first fluid and provided with projections on an innersurface thereof by pressing an outer surface of the core pipe, anddented portions that are formed on the outer surface of the core pipe; awinding pipe having a passage for communicating a second fluid separatedfrom the first fluid and being wound around the outer surface of thecore pipe; and a brazing material poured into the dented portions of thecore pipe proximate the winding pipe.
 2. The heat exchanger according toclaim 1, wherein the brazing material is in a paste form, which isapplied to the dented portions of the core pipe in advance and thenmelted and bonded thereto.
 3. The heat exchanger according to claim 1,wherein the brazing material is in a linear form, which is disposedbetween the core pipe and the winding pipe in advance and then is meltedand bonded thereto.
 4. The heat exchanger according to claim 1, whereinthe brazing material is in a linear form, which is disposed on thewinding pipe wound around the core pipe in advance and then melted andbonded thereto.
 5. The heat exchanger according to claim 1, wherein thebrazing material is in a paste form, which is applied to the windingpipe wound around the core pipe in advance and then melted and bondedthereto.